Interactions between parallel carbon nanotube quantum dots

Goß, Karin

Book	PreJuSER-136360

Interactions between parallel carbon nanotube quantum dots

Goß, K. (Corresponding author)FZJ*

2011
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
ISBN: 978-3-89336-740-5

Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag, Schriften des Forschungszentrums Jülich. Reihe Schlüsseltechnologien / key technologies 30, VIII, 139 S. (2011) = Universität Duisburg, Diss., 2011

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Please use a persistent id in citations: http://hdl.handle.net/2128/4522

Abstract: The subject of this thesis is molecular interactions which are investigated using the example of parallel quantum dots formed in the individual strands of a carbon nanotube rope. For molecular electronics, carbon nanotubes offer a variety of macromolecular structures and by combining several nanotubes into a rope, also a generic system to probe molecular interactions. First, the structure of the contacted rope is characterized by tip-enhanced Raman spectroscopy (TERS). We observe a clear resonance effect for the Raman scattering process, which is up to now not considered in the literature on TERS of carbon nanotubes. By extracting the diameter, metallicity and chirality, seven carbon nanotubes within the rope are identified. A redshift of their optical transition energies is attributed to interactions between the strands. In quantum transport measurements, the nanotubes are found to form interacting parallel quantum dots. Within the framework of master equations, a model is developed to describe the transport via the quantum dot system, where the parallel dots are capacitively and tunnel coupled. Employing this model, seven parallel quantum dots are characterized by their interactions. Along with changing interface properties predicted by the TERS characterization, the coupling to the two contacts is very asymmetric for most of the quantum dots. Additionally, the coupling to the gate electrode is found to vary strongly for individual dots, allowing one to tune the quantum dot system into different configurations and selectively add electrons to individual strands of the rope. Exploiting this differential gating effect, the magnitude of the molecular interactions can be investigated. Here, we find that individual strands within one carbon nanotube rope can interact very distinctly. Amongst the coupled quantum dots with a coupling stronger than previously assumed, we also find only capacitively interacting or completely uncoupled quantum dots within the one device. The tunnel coupling is a hybridization of quantum dot states which, in principle, are comprised of the molecular orbitals. In particular, the sign of the hybridization amplitude contains information about the involved wavefunctions, where we always find a negative amplitude denoting the overlap of wavefunctions with the same sign. The hybridization can be manipulated by an applied magnetic field and hence selectively suppressed due to spin effects. Here, the differential gating allows for tuning to distinct spin configurations of the quantum dot system. In conclusion, we demonstrate a tunable quantum device which provides the possibility of probing molecular interactions by quantum transport spectroscopy. The additional characterization using TERS represents a novel combination of two experimental techniques with great potential in the field of molecular electronics.

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